This invention relates to the drainage system art and more particularly to the drainage of enclosed areas in nuclear power plants.
A common drainage system includes a trap for each drain formed to retain enough liquid to prevent the upstream escape of downstream gases. Exemplary drain traps are the traps found below bathroom sinks. One disadvantage of this system is that a large gas pressure differential across the trap can cause the trap to "blow" its liquid and become ineffective.
An alternative to traps is the use of ball check-valves in place of the traps so that a high pressure downstream does not cause gas to escape. A disadvantage of the traps and check-valves of the prior art is that these valves accumulate solids and are easily clogged. Contamination of the valves with hazardous waste is especially undesirable in nuclear power plants due to the danger of high concentrations of radioactive contaminants. Therefore, an accumulation not amounting to blockage is a serious hazard in a nuclear environment.
In an effort to avoid the above disadvantages, other systems have been built without traps or valves but with means to ventilate drain gases and/or to provide a positive pressure differential between the enclosure and the drain system. These approaches have proven unreliable in practice.
There is a need, therefore, for a drain that can withstand relatively high pressure transients, does not accumulate large concentrations of hazardous radioactive contaminants, permits low-cost modification of existing systems not having traps or check-valves, and permits early detection and convenient removal of any waste accumulation in the drain.